Not sure if this is exclusive to Sydney and location specific.
Since the last 2 cycles, petrol stations from the whole area seem to rise price very suddenly AND at the same time. Eg. 121.9 at evening rush hour, 137.9 E10 before 9.00.
This is as opposed to the usual warning signs:
1. Petrol tankers come in, price then rises
2. Various companies may be one or 2 cents difference. Now all stations rise at exactly the same price.
3. The cycle was Thursday (in my area), now shifted to Wed
4. Petrol stations on one of the main road may go up first then the others follow and fix theirs.
Also, the price stays up longer, and the low price stays only one or 2 days which is much shorter than before.
Luckily years of OZB trained me with sharp eyes and sensitive radar. Found one that had raised the E10 to 137.9 while Premium 95 still at 135.9 and Unleaded at 122.9.
Does anyone know if, why and how this starts to happen?
The cycle is not weekly, it's more like 20+ days, sometimes modified by the onset of holidays. Check the graph here:
https://www.fuelcheck.nsw.gov.au/app
Also from the graph rises tend to be sudden and drops gradual.
This is very unusual as unleaded is usually more than E10. Are you remembering correctly? Same servo? Maybe they had only one pump with unleaded and it had run out?
I've been told about one indie servo at Haberfield on the side heading into the city that drops the price at night. So buyers heading home think I'll fill up tomorrow morning and then the next morning they find the price has gone up, but since it's on the cheaper side anyway, they go ahead and buy.